GB2306926A

GB2306926A - Control valve assembly for vehicle fluid pressure supply

Info

Publication number: GB2306926A
Application number: GB9523081A
Authority: GB
Inventors: Graham John Toogood
Original assignee: Ultra Hydraulics Ltd
Current assignee: Ultra Hydraulics Ltd
Priority date: 1995-11-10
Filing date: 1995-11-10
Publication date: 1997-05-14
Anticipated expiration: 2015-11-10
Also published as: GB2306926B; GB9523081D0

Abstract

A control valve assembly 1 comprises an inlet port 3 supplied by a pump 4, an outlet port 11 to an accumulator 10 and a braking or power steering system 9, an excess flow port 13 and a controlling spool valve 14. A pilot valve 32 supplies a signal to a port 25 of the spool valve 14 to control the valve depending on the pressure in the accumulator 10. The pilot valve 32 includes a pressure-sensing element 70 having a valve member 80 biased against a valve seat 82 and movable to engage a valve seat 83 when the pressure at port 74 exceeds a preset value to close off the pressure relief port 72 and so as to connect the output port 71 to the port 74. This assembly provides rapid switching between the open and closed positions of the control port 25 of the spool valve 14.

Description

"Hvdraulic Flow Control Valve Assemblies" This invention relates to hydraulic flow control valve assemblies, and is concerned more particularly, but not exclusively, with hydraulic flow control valve assemblies for supply of hydraulic fluid to vehicle power steering and accumulator charging systems.

GB 2277066A discloses a control valve assembly which permits priority flow from a pump to a first device, such as a power steering unit, as well as providing for fluid flow to a second device, such as an accumulator, as necessary, and providing excess flow as available to other services or tank. Such a control valve assembly is capable of supplying hydraulic fluid for operation of the power steering system of a forklift truck, for example, as well as supplying hydraulic fluid to charge an accumulator, such as is used in the braking system of a forklift truck, for example, when the accumulator pressure falls to a level indicating that charging of the accumulator is required. Such a combined control valve assembly is efficient in operation and can be made particularly compact.

It is an object of the invention to provide an improved hydraulic flow control valve assembly.

According to the invention there is provided a hydraulic flow control valve assembly as defined by the accompanying claims.

In order that the invention may be more fully understood, a preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing in which the single figure is a schematic diagram of the control valve assembly.

The control valve assembly 1 shown in the drawing is a modification of the control valve assembly described with reference to the drawings of GB 2277066A, and the same reference numerals as are used in the drawings of the earlier application are used in the drawing of the present application to denote similar parts. The control valve assembly 1 shown in the drawing will be described for controlling the charging of an accumulator 10 of a braking system. However it will be appreciated that the control valve assembly illustrated can be used for supplying hydraulic fluid to both a power steering unit and an accumulator, as described with reference to the drawings of the earlier application, or alternatively simply for supplying hydraulic fluid to a power steering unit.

Referring to the drawing, the control valve assembly 1 comprises a spool valve 14 having an inlet port 3 connected to a pump 4, such as a gear pump, a priority outlet port 11 for charging of an accumulator 10 for supplying hydraulic fluid by way of a brake port 9 to a braking system, an excess flow port 13 for supply of excess fluid to other services or tank, and a spool member 15 for controlling fluid flow through the spool valve 14.

The spool valve 14, which is described in greater detail in GB 2277066A, has a bore 16 within which the spool member 15 is slidable, and a spring 17 biassing the spool member 15 towards the left as shown in the drawing. The spool member 15 has annular grooves 19 and 21 communicating with the outlet port 11 and the excess flow port 13, an axial passage 22, and radial passages 24 interconnecting the axial passage 22 and the annular groove 19. A control port 25 communicates with one end of the bore 16, and an end chamber 30 provided at the other end of the bore 16 communicates with the axial passage 22. A restriction orifice 56 is provided in the outlet port 11, and a bypass passage 59 opening into the outlet port 11 downstream of the restriction orifice 56 incorporates a further restriction orifice 60.

A pilot valve portion 32 is provided for supplying a fluid control signal to the control port 25 of the spool valve 14 in order to control charging of the accumulator 10. The pilot valve portion 32 comprises a pressure sensing element 70 having an output port 71, a pressure relief port 72 connected to tank 73, and a pressure sensing port 74 connected to the output of the accumulator 10, and a switching element 75 having an output port 76 connected to the control port 25 of the spool valve 14, a pressure relief port 77 connected to tank 78, and an input port 79 connected to the output port 71 of the pressure sensing element 70.

The pressure sensing element 70 incorporates a ball valve member 80 disposed within a valve chamber 81 between first and second valve seats 82 and 83, the valve member 80 being biased into engagement with the first valve seat 82 by a push rod 84 which is connected to a piston 85 acted upon by a compression spring 86 and slidable within a cylinder 87 so as to support the push rod 84 centrally within the second valve seat 83 such that, when the valve member 80 is in engagement with the first valve seat 82, the second valve seat 83 defines an annular passage around the push rod 84 for fluid flow to tank 73. The switching element 75 incorporates a spool actuator 88 displaceable within a bore 90 against the action of a compression spring 89 in response to fluid pressure applied to the input port 79.The actuator 88 incorporates an annular groove 91 which, when the actuator 88 is aligned with the output port 76 and the pressure relief port 77, serves to connect the control port 25 of the spool valve 14 to tank 78.

The manner in which the control valve assembly 1 operates to charge the accumulator 10 will now be described. At start up, if the accumulator 10 is discharged, the control valve assembly 1 must first operate to charge the accumulator 10 with hydraulic fluid from the pump 4. At this stage the valve member 80 of the pressure sensing element 70 closes off the first valve seat 82 as shown in the drawing, thus connecting the input port 79 of the switching element 75 to tank 73 by way of the second valve seat 83, with the result that the spool actuator 88 is in the position shown in the drawing closing off the output port 76 of the switching element 75 and the control port 25 of the spool valve 14.The spool member 15 of the spool valve 14 is thus held by the spring 17 in the position shown in the drawing in which fluid is conducted by the pump 3 by way of the annular groove 19 to the outlet port 11 so as to supply a constant flow of fluid to charge the accumulator 10.

Charging of the accumulator 10 results in an increase in the output pressure of the accumulator, and, when the accumulator output pressure reaches a pre-set level, the pressure at the pressure sensing port 74 of the pressure sensing element 70 causes displacement of the valve member 80 against the action of the spring 86 so as to lift the valve member 80 from the first valve seat 82 and engage it with the second valve seat 83, thus closing off the input port 79 of the switching element 75 from tank 73 and connecting it to the accumulator output.As a result accumulator output pressure is supplied by way of the pressure sensing element 70 to the input port 79 of the switching element 75 so as to displace the spool actuator 88 against the action of the spring 89 to a position in which the groove 91 is aligned with the output port 76 and the pressure relief port 77, thus connecting the control port 25 of the spool valve 14 to tank 78 and unloading the right hand end of the spool member 15. The fluid pressure in the end chamber 30 acting on the opposite end of the spool member 15 therefore moves the spool member 15 to the right against the action of the spring 17 so as to stop further fluid flow to the accumulator 10 and provide further fluid flow from the pump 4 by way of the groove 21 to the excess flow port 13.

As long as the control port 25 is closed off by the switching element 75 during charging of the accumulator 10, the pressure drop across the orifices 56 and 60 ensures that the pressure acting on the left hand end of the spool member 15 is greater than the pressure acting on the right hand end of the spool member 15, and, if the flow through the orifice 56 is high enough, this pressure difference will be sufficient to overcome the action of the spring 17 so as to cause the valve member 15 to move towards the right so as to direct at least some of the pump flow towards the excess flow port 13. The flow rate to the accumulator 10 is therefore controlled by the orifice 56 and the loading of the spring 17 so that the spool member 15 is caused to take up a position at which a constant pressure drop across the orifice 56 is maintained.

As the braking system is operated in use, fluid is drained from the accumulator 10 so that the accumulator output pressure reduces until such time as it is insufficient to hold the valve member 80 of the pressure sensing element 70 in engagement with the second valve seat 83 with the result that the valve member 80 is lifted off the second valve seat 83 by the action of the spring 86 and engaged with the first valve seat 82. The accumulator output pressure at which this will occur is less than the pressure at which the valve member 80 is lifted off the first valve seat 82 in order to initiate accumulator charging, since the throughflow cross-section of the first valve seat 82 is less than the through flow cross-section of the second valve seat 83.Such displacement of the valve member 80 again connects the input port of the switching element 75 to tank 73 by way of the second valve seat 83 with the result that the spool actuator 88 is returned by the spring 89 to the position in which the control port 25 of the spool valve 14 is closed off and the spool member 15 is moved to the left by the spring 17 to cause re-commencement of accumulator charging.

The combination of the pressure sensing element 70 and the switching element 75 constituting the pilot valve portion 32 as described above is advantageous because it provides well defined and rapid switching between the open and closed positions of the control port 25 of the spool valve 14, whilst enabling the pressure sensing element 70 and the switching element 75 to be produced in a straightforward manner and integrated in a single block so as to be of compact construction. By contrast the pilot valve portion of the control valve assembly shown in the drawings of GB 2277066A suffers from the disadvantage that the valve member allows some leakage to occur prior to opening of the valve as well as being prone to jamming under certain conditions.

Claims

1. A hydraulic flow control valve assembly comprising an inlet port for input fluid flow from a pump, an outlet port for output fluid flow to a fluid pressure actuated device, an excess flow port for excess output fluid flow, flow control means for controlling the fluid flow from the inlet port to the outlet port and the excess flow port, and pilot valve means for supplying a fluid control signal to a control port of the flow control means so as to cause the flow control means to supply fluid to the outlet port in a first state of the fluid pressure actuated device and to inhibit fluid flow to the outlet port in a second state of the fluid pressure actuated device, wherein the pilot valve means includes a pressure sensing element having an output port, a pressure relief port, a pressure sensing port for connection to the fluid pressure actuated device, and a valve member disposed within a valve chamber between first and second valve seats and biased into engagement with the first valve seat so as to close off the pressure sensing port and so as to connect the output port to the pressure relief port by way of the second valve seat, the valve member being movable out of engagement with the first valve seat and into engagement with the second valve seat when the pressure applied to the pressure sensing port exceeds a preset value so as to close off the pressure relief port and so as to connect the output port to the pressure sensing port by way of the first valve seat.

2. An assembly according to claim 1, wherein the pilot valve means additionally includes a switching element having an output port connected to the control port of the flow control means, a pressure relief port, an input port connected to the output port of the pressure sensing element, and an actuator movable in response to a pressure change at the input port between a position connecting the control port to the pressure relief port of the switching element and a position closing off the connection to the control port.

3. An assembly according to claim 2, wherein the switching element is arranged to connect the control port to the pressure relief port of the switching element when the valve member of the pressure sensing element is in engagement with the first seat so as to cause the flow control means to supply fluid to the fluid pressure actuated device, and to close off the connection to the control port when the valve member of the pressure sensing element is in engagement with the second seat so as to cause the flow control means to inhibit fluid flow to the fluid pressure actuated device.

4. An assembly according to claim 1, 2 or 3, wherein the first valve seat of the pressure sensing element has a smaller through flow cross-section than the second valve seat so that the valve member of the pressure sensing element is moved into engagement with the second valve seat to close off the pressure relief port at a pressure applied to the pressure sensing port which is higher than the pressure at which the valve member is moved into engagement with the first valve seat in order to close off the pressure sensing port.

5. An assembly according to any preceding claim, wherein the valve member of the pressure sensing element is a ball which is positioned between the first and second valve seats which face one another on opposite sides of the valve chamber and which is biased into engagement with the first valve seat by a push rod extending through the second valve seat.

6. An assembly according to claim 5, wherein the push rod is connected to a piston which is acted on by a spring so as to urge the push rod into contact with the valve member and to thereby bias the valve member into engagement with the first valve seat, the piston being slidable within a cylinder and supporting the push rod centrally within the second valve seat so as to provide an annular passage around the push rod for fluid flow to the pressure relief port when the second valve seat is open.

7. An assembly according to any preceding claim, wherein the flow control means is a spool valve having a spool member which is biased by a spring towards a position in which fluid is supplied from the inlet port to the outlet port of the flow control means.

8. A vehicle braking system incorporating an accumulator and a hydraulic flow control valve assembly according to any one of claims 1 to 7 for charging the accumulator.

9. A vehicle steering system incorporating a power steering unit and a hydraulic flow control valve assembly according to any one of claims 1 to 7 for supplying hydraulic fluid to the power steering unit.

10. A hydraulic flow control valve assembly substantially as hereinbefore described with reference to the accompanying drawing.

Amendments to the claims have been filed as follows

1. A hydraulic flow control valve assembly comprising an inlet port for input fluid flow from a pump, an outlet port for output fluid flow to a fluid pressure actuated device, an excess flow port for excess output fluid flow, flow control means for controlling the fluid flow from the inlet port to the outlet port and the excess flow port, and pilot valve means for supplying a fluid control signal to a control port of the flow control means so as to cause the flow control means to supply fluid to the outlet port in a first state of the fluid pressure actuated device and to inhibit fluid flow to the outlet port in a second state of the fluid pressure actuated device, wherein the pilot valve means includes a pressure sensing element having an output port, a pressure relief port, a pressure sensing port for connection to the fluid pressure actuated device, and a valve member disposed within a valve chamber between first and second valve seats so as to be selectively engageable with the first and second valve seats, the valve member being biased into engagement with the first valve seat so as to close off the pressure sensing port and so as to connect the output port to the pressure relief port by way of the second valve seat, and the valve member being movable out of engagement with the first valve seat and into engagement with the second valve seat when the pressure applied to the pressure sensing port exceeds a preset value so as to close off the pressure relief port and so as to connect the output port to the pressure sensing port by way of the first valve seat.

4. An assembly according to claim 1, 2 or 3, wherein the first valve seat of the pressure sensing element has a smaller throughflow cross-section than the second valve seat so that the valve member of the pressure sensing element is moved into engagement with the second valve seat to close off the pressure relief port at a pressure applied to the pressure sensing port which is higher than the pressure at which the valve member is moved into engagement with the first valve seat in order to close off the pressure sensing port.

9. A vehicle steering system incorporating a power steering unit and a hydraulic flow control valve assembly according to any one of claims I to 7 for supplying hydraulic fluid to the power steering unit.